My problem was mechanical and would occur at 10 watts drive. Suddenly my PTT
would not function. It was the same in CW or SSB.
Hence my thought of a bad RCA connector or faulty relay contacts. The former,
more likely, looks like it was the culprit.
If the PTT worked I haven't had a problem when running power. I do agree that
K6 is pretty close to some traces.
73,
Rick
VE7TK
Subject: Re: [TenTec] 253 Keying Loop - Intermittent From: Ken
Brown
Date: Sat, 01 Sep 2007 14:27:22 -1000
Hi Rick,
K6, the relay that interrupts the keying loop (the exciter in / exciter
out path) in the 253 is located on the the same PCB as the KW (SWR)
Bridge. In my opinion the keying loop traces are way too close to the
high power RF paths on that board. When I had my keying loop running
through my 253 I had some difficulties too. Removing the 253 from the
loop made the keying problems go away, but then the 253 no longer has
the ability to prevent keying when it detects a high SWR or other fault
condition. I thought about trying to make some kind of a shield out of
copper sheet or PCB material, and installing it between K6, R7 and rest
of the components on that board. I have not tried it yet.
My guess that RF pick up by the keying loop as it passes through the
81486 board is causing the problem does not seem to be supported by the
fact that you could make the problem go way by wiggling the cables or
resoldering connections. Still I think it would be better if there were
some shielding between the RF and keying loop on that board.
N6KB
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